Add include inverse mappings to ExifTags docs.

docs/reference/ExifTags.rst

@@ -4,25 +4,45 @@
 :py:mod:`~PIL.ExifTags` Module
 ==============================
 
-The :py:mod:`~PIL.ExifTags` module exposes two dictionaries which
+The :py:mod:`~PIL.ExifTags` module exposes four dictionaries which
 provide constants and clear-text names for various well-known EXIF tags.
 
 .. py:data:: TAGS
     :type: dict
 
-    The TAG dictionary maps 16-bit integer EXIF tag enumerations to
+    The TAGS dictionary maps 16-bit integer EXIF tag enumerations to
-    descriptive string names.  For instance:
+    descriptive string names. For instance:
 
         >>> from PIL.ExifTags import TAGS
         >>> TAGS[0x010e]
         'ImageDescription'
+        
+.. py:data:: TAG_CODES
+    :type: dict
+
+    The TAG_CODES dictionary maps descriptive string names to 16-bit integer EXIF
+    tag enumerations. For instance:
+
+        >>> from PIL.ExifTags import TAG_CODES
+        >>> TAG_CODES['ImageDescription']
+        0x010e
 
 .. py:data:: GPSTAGS
     :type: dict
 
     The GPSTAGS dictionary maps 8-bit integer EXIF gps enumerations to
-    descriptive string names.  For instance:
+    descriptive string names. For instance:
 
         >>> from PIL.ExifTags import GPSTAGS
         >>> GPSTAGS[20]
         'GPSDestLatitude'
+        
+.. py:data:: GPS_CODES
+    :type: dict
+
+    The GPS_CODES dictionary maps descriptive string names to 8-bit integer EXIF
+    gps enumerations. For instance:
+
+        >>> from PIL.ExifTags import GPSTAGS
+        >>> GPS_CODES['GPSDestLatitude']
+        20